The present invention relates to self-aligning peptides modeled on human elastin and other fibrous proteins. The peptides are useful, for example, as biocompatible material for implantation into humans, or for elastic materials.
Currently available synthetic implant materials for soft tissue prosthesis fall short of optimal biocompatibility. The ideal material would provide appropriate structural support, would be biocompatible, in the sense of causing no immunogenic or thrombogenic response, would mimic the physical properties of the tissue replaced, and would provide a friendly environment for normal cell infiltration and growth.
While tissue can sometimes be borrowed from another part of the patient's body, such as by skin grafting or blood vessel replacement, this approach has several limitations, including the limited availability of appropriate donor tissue. Synthetic materials such as dacron, teflon (Gortex) and polyurethane, as well as metals (such as stainless steel and titanium), often are used for prostheses of soft tissues. While these materials can meet the requirements of strength, durability, and flexibility, as foreign materials they are not maximally biocompatible for long term use.
One approach to dealing with this problem has been to coat non-biological materials with proteins or other natural substances. Another approach has been to use biological materials from animal tissue preparations. For example, animal skin preparations have been used to cover burns, and processed animal blood vessels have been used to provide potential blood vessel replacements for humans.
Elastin, a natural structural protein, has received considerable attention for potential use in prostheses, both in soluble forms for coating non-biological prostheses, and in solid forms to produce biologically-derived prostheses. Elastin has structural properties which make it suitable for use in prosthesis and it provides a biocompatible, non-thrombogenic surface for cell infiltration. It is a durable, extremely stable, and highly insoluble extracellular matrix protein which imparts the properties of extensibility and elastic recoil to tissues in which it is found, including large blood vessels, elastic ligaments, lung parenchyma, and skin.
Large arteries are a good source of elastin. Because human arteries are not available in quantity, however, animal arteries have been the primary source of elastin. Because arterial elastin is a highly insoluble matrix, soluble elastin-derived material is generated by treating the insoluble protein with acid or alkali, producing hydrolyzates such as alpha- and kappa-elastin. These are relatively undefined mixtures of peptides of mixed sizes.
In attempts to develop biocompatible materials, soluble animal elastin materials have been used to coat non-biological prosthetic materials, usually with fixation by chemical cross-linking agents. For example, U.S. Pat. No. 4,960,423 (Smith) is directed to a synthetic vascular prosthesis coated with a water-soluble peptide derived from animal elastin.
U.S. Pat. No. 5,416,074 (Rabaud) is directed to a composition comprising elastin or a solubilized elastin peptide and another connective tissue protein, such as fibrin. The solubilized elastin peptide has a molecular weight of greater than 10,000.
U.S. Pat. No. 4,474,851 (Urry) is directed to an elastomeric composite material comprising an artificial core fiber, such as Dacron, and a polypeptide comprising repeating tetrapeptide or pentapeptide units. The units are derived from units observed to be repeated in the tropoelastin molecule, Val-Pro-Gly-Val-Gly (VPGVG) (SEQ ID NO:6) and Val-Pro-Gly-Gly (VPGG) (SEQ ID NO:7). The polypeptide comprises a series of beta-turns and is proposed to have a beta-coil structure. The polypeptide provides elastomeric properties to the composite material, but has little structural strength or integrity. The artificial core fiber provides these latter properties to the composite material.
U.S. Pat. No. 4,979,959 (Guire) is directed to a method of improving the biocompatibility of solid biomaterials by coating them with biocompatible agents and chemically linking the biocompatible agents to the surface via a photochemical reaction.
Elastin-based materials also have been used to produce solid materials from which prostheses can be manufactured. These include soluble animal elastin co-aggregated with other proteins such as collagen, fibrin, fibronectin and laminin, to produce gel-like materials, and polymerized materials derived from short hydrophobic sequences of human elastin (such as PGVGVA) (SEQ ID NO:5). In some cases, these synthetic peptides also include short alanine-rich sequences containing lysine residues, allowing cross-linking between the elastin-like peptides or to other proteins such as collagen. Both elastin and collagen contain crosslinks derived from lysine. For example, U.S. Pat. No. 5,223,420 (Rabaud) is directed to an elastin-based product comprising an adduct containing elastin and at least one other protein, such as fibrin.
U.S. Pat. No. 4,589,882 (Urry) is directed to an artificial elastomeric copolymer comprising an elastomeric component of repeating units of tetrapeptides and pentapeptides and a crosslinking component which may comprise amino acid residues. The repeating units are derived from elastin. U.S. Pat. No. 4,132,746 (Urry) is directed to a synthetic, insoluble, crosslinked polypentapeptide. The pentapeptide is the VPGVG peptide present in tropoelastin. See also U.S. Pat. No. 4,500,700, U.S. Pat. No. 4,870,055, and U.S. Pat. No. 5,250,516 (all to Urry) for other materials derived from this peptide. The polypeptides described in these patents comprise a series of beta-turns and are proposed to have a beta-coil structure.
Animal arteries also have been stripped of extraneous material, leaving largely a matrix of elastin and collagen in tubular form that can be used for blood vessel replacement. For example, U.S. Pat. No. 4,776,853 (Klement) is directed towards a process for preparing an implantable biological material from suitable donor tissue.
The respective contents of the above-described patents and publications are incorporated by reference herein in their entirety.
The materials discussed above were developed to satisfy the need for prostheses suitable for implantation into humans. These materials are not completely satisfactory, however, and there remains a need for prosthesis which have appropriate mechanical properties and which can be used in contact with blood, tissue fluids and cells without adverse effects.